The present invention relates to a volume control apparatus associated with an electronic musical amplifier and speaker. The system of this invention is for maintaining a constant distortion output over the volume range of the speaker system. Furthermore, the system of this invention provides a low cost, high power speaker volume control that may be remotely located from the amplifier. A further characteristic of the present invention is the provision for a relatively simple circuit to accomplish the task and that is quite easy to operate.
My U.S. Pat. No. 4,143,245 shows a volume control arrangement which has worked effectively but has certain disadvantages associated therewith. For example, when connected with a predetermined ohmage speaker, there is provided a separate selector switch that may have to be changed from position to position depending upon the volume setting. This has been found to be a further requirement of the performer that is undesirable. Furthermore, with this power of volume control, in the maximum volume position selected, there is still some power reduction because of a resistance remaining in parallel with the speaker.
Another arrangement that is provided for volume control to a speaker is an attenuating potentiometer which is coupled in parallel with the speaker between the amplifier and the speaker. The problem with this arrangement is that there is a wide variation in the input impedance of the potentiometer and speaker combination as presented to the driving source, typically the output from a power amplifier. Also, as mentioned previously in connection with the volume control described in my patent, in the maximum position there is a power reduction because of resistance in parallel with the speaker.
Another arrangement used to provide volume control to a speaker is an "L" or "T" attenuator circuit. This type of control is inherently expensive because two interconnected potentiometers are required. Also, this type of control does not allow volume settings up to full power of the amplifier because at least one potentiometer is wired in parallel with the speaker in the maximum volume position.
Accordingly, one important object of the present invention is to provide a volume control for a speaker which maintains the input impedance to the control network in approximately the same range as the speaker impedance, or at a desired predetermined impedance. In a worst case condition, the input impedance is maintained to within about 30% to -5% of the speaker impedance.
Another object of the present invention is to provide a volume control that eliminates the use of a potentiometer for volume control. With constant use, potentiometers tend to develop dead spots thus making volume control non-repeatable and non-uniform; also, extreme settings on potentiometers require high current capacities which usually dictate the use of a potentiometer rated to dissipate three or four times the maximum power actually applied to it. This also means, of course, that relatively large size potentiometers are necessary.
Another object of the present invention is thus to provide a volume control for a speaker that is not large and cumbersome and that can be light in weight, packaged in a relatively small container, and that can be made relatively inexpensively.
Still another object of the present invention is to provide a volume control for a speaker that has good heat dissipation characteristics.